The present invention concerns a clamped resonator fabricated from a quartz substrate having a ZT-cut.
A ZT-cut piezo-electric resonator, to which the present invention applies, has been described in U.S. Pat. No. 4,313,071. It is fabricated from a thin rectangular quartz plate whose length, width and thickness are orientated along axes X', Y' and Z' respectively. The Z'-axis is situated in the plane containing the electrical, X, and optical, Z, crystal axes and forms an angle, .phi., with the Z-axis such that 16.degree.&lt;.phi.&lt;36.degree. and the Y'-axis forms an angle, .theta., with the mechanical Y-axis such that 10.degree.&lt;.theta.&lt;30.degree.. Such a resonator vibrates in a contour mode and possesses excellent temperature characteristics. In particular, the first-order temperature coefficient is zero and does not depend critically on the plate's dimensional ratio w/l and the higher-order temperature coefficients are very small. Until now, such a resonator had to be mounted with suspension wires fixed at neutral points. Such a construction is delicate and leads to limited shock resistance as well as a high final cost.
Available on the market are quartz crystals with different cuts, among which the GT-cut is that which possesses the most favorable temperature characteristics. A GT-cut resonator consists of a thin rectangular plate and vibrates in a contour mode. A resonator of this type, fabricated in a way which allowed it to be easily mounted, has been described at the 34th Annual Frequency Control Symposium, USA ERADCOM, Ft. Monmouth, NJ 07703 in May 1980 under the title: "New frequency temperature characteristics of miniaturized GT-cut quartz resonators". The described resonator consists of a thin rectangular plate on whose sides supporting portions have been fabricated. These supporting portions are complex and add to the inherent critical nature of the temperature characteristics of a GT-cut quartz crystal. In effect, the temperature characteristics depend in a critical way on the plate's dimensional ratio and also on the size of the supporting portions. As these dimensions are very small (typically 80 .mu.m for the width of the support), fabrication tolerances necessarily imply an individual adjustment of the temperature characteristics for each resonator, which increases the final cost.